1. Field of the Invention
This invention relates to telecommunications and, more particularly, to a telecommunications wiring device and system for providing reliable analog and digital transmission of electrical signals, using componentry capable of operating at Level 5 (100 Megabits per second) where desired.
2. Related Art
Existing office telecommunications wiring systems are directed either to (1) a conventional hard-wired system which requires a technically skilled person for configuration or reconfiguration of an office telecommunications network or (2) a system such as that described in U.S. Pat. No. 5,272,277 ("the '277 patent") issued to Humbles et at., which is hereby incorporated by reference in its entirety, which allows a technically unskilled person to configure or reconfigure an office telecommunications network through the use of modular reusable devices.
The conventional method of telecommunications wiring is extremely costly because it requires a substantial amount of time and labor for a skilled technician to physically place a line from a local telephone company distribution/demarcation block to each individual user telecommunications device (such as a telephone, telefax or computer). The system described in the '277 patent represents an extreme improvement over the conventional method in that it uses a modular, reusable format to install the transmission media instead of hardwiring each device. Use of the '277 system eliminates the need for a highly skilled technician and enables an untrained technician to reconfigure an office telecommunications network quickly and easily. It should be noted that this system can be used for both telephonic analog and computer digital communication.
Because many conventional computers transmit and receive data at a rate of 10 Mbps or 16 Mbps, digital transmission of computer signals may be accommodated by the traditional method or the '277 system. However, the wiring system of the '277 patent is superior because of increased speed of reconfiguration, reduced expense of administrative record keeping, and lowered costs associated with employing an unskilled technician.
More recently, various "information highways" have been established on local area networks and wide area networks. Computing power has increased tremendously because of successive generations of Very Large Scale Integration ("VLSI") chips while its costs have dropped dramatically. These factors have helped increase demand for the same, thereby increasing the volume of information transmitted. The increase in volume of information transmitted coupled with technological improvements have created a need for an increased rate of digital transmission.
In particular, a transmission rate known in the art as "Level 5," or 100 Mbps, is increasingly required. The challenge is to provide physical facilities which can achieve this transmission rate reliably. The greatest barriers to achieving this transmission rate are presented by Attenuation, NEXT (Near End Crosstalk), Noise and Capacitance.
Attenuation is the signal loss on twisted-pair cable. Poor quality RJ45 block connections can lead to excessive resistance and attenuation. This may be corrected by making sure that each of the conductors are seated completely within the connection and that the correct type of connector/wire combination (stranded or solid) is used. Excessive length may also cause signal loss which may be corrected by adding a repeater or eliminating excessive cable coiled in ceilings or wiring closets. It is also prudent to verify that the length of the conductors fall within manufacturer's guidelines for the network. Where patch cables are necessary, use high grade cables with a minimum length possible as use of non-twisted pair patch cables, i.e., Silkline, can adversely effect results.
NEXT, or Near End Crosstalk, is a measure of the amount of signal which "leaks" from the station's (or hub's) transmitter to its own receiver. Most of this leakage occurs between the transmit pair and the receive pair and is symmetric (e.g., 12-36 NEXT is always the same as 36-12 NEXT). To measure NEXT, signals of known amplitude and frequency are transmitted on each pair within the cable in succession. The amount of signal coupled to adjacent pairs is measured and reported as NEXT. The frequency range used to measure NEXT varies among different network topologies. The following table lists frequency test ranges for common network types:
______________________________________ Network Topology NEXT Frequency Range ______________________________________ 4 Mbps Token Ring 1.0 .about. &gt; 4.0 Mhz 16 Mbps Token Ring 4.0 .about. &gt; 16.0 Mhz 10 Base T 5.0 .about. &gt; 10.0 Mhz Custom Twisted-Pair 1.0 .about. &gt; 20.0 Mhz ______________________________________
The test signals are transmitted by sweeping the frequency range and NEXT is measured for each of the pairs. The worst case NEXT and the frequency at which it occurred is used to determine whether the pair meets or exceeds test limits. Possible causes of an unacceptable NEXT reading can be traced to excess cable looped in Token Ring Hub, defective couplers, poor grade of cable, defective patch cables, improper pair twists, and split pairs.
Resistance is measured by measuring a loop through each pair in the cable. For example, the value reported in ohms for pins 1, 2 is the resistance from pin 1 in the cable looped to pin 2. During testing, resistance is said to fail if measured resistance values on pairs used by the Network Type selected is greater than the resistance for a maximum length loop (100 meters for most networks).
Noise is an effect on a signal from outside sources. A Scanner may measure the electrical noise on a cable to verify that noise levels do not interfere with LAN performance. Unshielded twisted-pair (UTP) is particularly sensitive to noise in its environment. Noise is measured in three frequency bands to help isolate possible sources:
______________________________________ Noise Band Frequency Range Possible Source ______________________________________ Low 10 .about. &gt; 150 Khz Fluorescent lights, Mid 150 Khz .about. &gt; 16 Mhz Motors, video, etc. High 16 Mhz .about. &gt; 100 Mhz Radio, TV ______________________________________
The effects of excessive capacitance on a Level 5 transmission circuit are disastrous. Excessive capacitance will create a delay in the transmission of the digital signal, a catastrophic effect in light of the narrow time gap between digital pulses which are transmitted at a rate of 100 million bits per second. As a result, excess capacitance will bring a Level 5 circuit "down."
It is well known in the art that an electrical circuit based on direct current voltage is adversely affected by the addition of a capacitor in that the capacitor creates a time delay in the current traveling around the circuit. In the context of the present invention, digital signal transmission is based on direct current voltage provided by either the local telephone company ("telco") or a computer. Predictably, digital transmission of Level 5 signals is distorted by excess capacitance in the circuit. Computer transmission of digital signals is accomplished over a telecommunications network which utilizes the telephone "pair" system. Because these pairs are long, i.e., stretch in parallel for long distances, each pair behaves like a capacitor. To minimize the effects of capacitance in wires and a cable, telecommunications cable is currently manufactured so that the wires comprising each pair are carefully and individually twisted in a way which decreases the effects of said capacitance.
However, excess capacitance is also created by a telephone pair of wires which are in "multiple" with the desired transmission path. The term "multiple" is known to those skilled in the art as the term which identifies when the "count" of the transmission element or wire is the same, thus indicating more than one possible transmission path. For example, when a feeder pair, A, is joined to two distribution pairs, B and C, pair B is in multiple with pair C. Thus, when a telephone or other telecommunications device is placed on the end of pair C, pair B creates capacitance on the circuit. Pair B is known in the art as "bridge tap."
Bridge tap may be avoided by having a skilled technician place a separate line from the telco distribution/demarcation block to each user individual telecommunications device, such as a computer or telephone. However, administrative records must be constantly maintained in the event a person changes office locations. Further, reconfiguration of the network is expensive and time consuming.
In the '277 patent, extraordinarily fast reconfigurations of an office telephone network is achieved because, for example, pair one which is assigned to the first work station picks off the feeder cable from the Telco distribution punch down block. However, while pair one serves as a transmission path for the first work station, pair one also appears in other work stations to the field side of the initial connection between the first work station's Xtractor assembly and the feeder cable. The portion of pair one extends to the distribution side is therefore not used for direct transmission of a signal from the user telecommunications device and a bridge-tap is formed. This bridge-tap may cause Level 5 LAN environments to fail. Based on this inventor's experience, six feet of bridge-tap or more will cause transmission failure of signals at these greater speeds. As a result, the wiring system disclosed in the '277 patent is unsuitable for Level 5 or higher transmission rates. Therefore, there is a need in the art to provide a wiring device and wiring system which may be physically placed by an unskilled technician and yet will support these higher rates of transmission.
Near End Cross Talk also causes Level 5 transmission circuits to fail. The inventor has determined that a db level of approximately 18 will cause such a failure. As the 18 db cutoff is approached, performance of the Level 5 system declines. It has been discovered that certain connectors having db levels of approximately 40 will perform well at Level 5, but multiple connectors attached in series cause decreased performance at Level 5. Prior art diversion leads terminated on prior art connectors are typically terminated at staggered pin positions. Therefore, a db level approaching 50 db or more is highly desirable in that multiple connectors could be attached in series while maintaining high quality performance at Level 5.
The present invention provides a telecommunications wiring device which overcomes the shortcomings of the known telecommunications wiring systems by providing a telecommunications device capable of normal analog voice transmission as well as reliable data transmissions without a bridge-tap and with a high NEXT db measurement, while being also capable of being placed physically by an unskilled technician.